2) As a result (for physical reasons, which would take longer
to explain), the arrangement of the keys on Linotype typesetting
machines was not QUERTY, but frequency arranged columns: ETAOIN
was the first column (reading downward), SHRDLU the second, etc.

3) The Linotype (which produced slugs of hot type metal from
brass molds) did not have a backspace. It was a complicated process
to get rid of a mistyped line.

4) So when they made a mistake, lazy linotypists would fill
the rest of the line with garbage, so it would get pulled later
by the proofreaders (lines of type were metal objects).

5) What is the easiest way to fill a line with random characters?
(exercise left to the reader).

6) Not all proofreaders are alert. Therefore lines full of
things like SHRDLUSHRDLUSHRDLU occasionally found their way into
print (I have a collection of odd clippings that people sent me
over the years -- they have long since stopped coming, as computer
typesetting replaced the Linotype).

7) MAD
Magazine authors picked up these sequences as nonsense words
and used them as you mention above.

8) I read MAD in my youth.

9) When it came time to name the system, I tried to come up
with acronyms and none were very good so I decided to just pick
something that looked like an acronym but wasn't. I reached into
my memories for a random sequence.

10) Several years later, someone gave me a copy of the science
fiction story by Frederic
Brown, written originally in 1942(!), entitled "ETAOIN
SHRDLU" in which an artificially intelligent Linotype
machine (with natural language ability) learns everything it typesets
and tries to take over the world (World of Wonder ed. Fletcher
Pratt (New York: Twayne, 1951, $3.95, 445pp, hc)). When I saw
it, it seemed vaguely familiar, so I suspect that I had read it
during my science-fiction years in high school, and it had stuck
somewhere in the dim recesses of my memory and popped back out
when appropriate.

--t

p.s., the hero outwits ETAOIN SHRDLU by having it typeset every
book on Buddhism. The story ends: "See, George, it believes
what it sets. So I fed it a religion that convinced it of the
utter futility of all effort and action and the desirability of
nothingness...It doesn't care what happens to it and it doesn't
even know we're here. It's archived Nirvana, and it's sitting
there contemplating its cam stud."